Line conduits are employed when structural elements are built using concrete or another liquid construction material so that openings in floors/ceilings or walls for lines such as, for instance, cables or pipes can be kept free in the structural elements or else can be integrated in them. The line conduits are positioned in a mold (formwork) into which the liquid construction material is filled, and they keep the desired opening in the structural element free while the construction material is being filled in.
The line conduits can also be removed once the construction material has hardened. However, they are often left in the wall and additional elements, for example, seals or fire-protection elements, are arranged in them so that the wall or floor/ceiling can be closed in case of a fire. The fire-protection element can be made of an intumescent material whose volume expands under exposure to heat, thus closing the wall opening.
The fire-protection element can be positioned in such a way that, once the wall or floor/ceiling is finished, it is situated on the surface of the structural element. As a result, the presence of heat will quickly heat up and activate the intumescent material.
This is particularly advantageous for a floor/ceiling opening. Plastic tubes that pass through such a floor/ceiling soften very quickly upon exposure to heat, forming a drop-shaped constriction below the insulating fire-protection element. The remaining, soft plastic tube is compressed and sealed off by the expanding fire-protection element. The tube that remains below the fire-protection element continues to melt or drops off due to gravity, while the fire-protection element, which continues to expand, is pressed into the section that remains in the line conduit.
This creates a stable bond between the remaining line section and the intumescent material. This entails the advantage that the fire-protection element is affixed and stabilized in the line conduit by the line section. Therefore, after the conduit has been heated up and sealed, there is sufficient stability to withstand, for example, a jet of water that is aimed directly at the fire-protection element.
In order to achieve a smooth wall finish, the fire-protection element is often arranged not on but rather in the opening in the wall or the floor/ceiling, so that the fire-protection element does not project beyond the surface of the structural element. This has the advantage that such a fire-protection element can be cast into the structural element while it is being made.